In the field of oil well drilling technology, power tongs are used to turn and make-up or break joints on tubing or drill rod as small as on the order of 1 inches in diameter, and on pipe or casing ranging up to 16 inches in diameter or more. Hereafter in this specification, all such tubing and rod whether for use in the oilfield or otherwise are collectively referred to as “pipe”.
As an example of a power tong of the type which may be re-adapted to employ the invention herein, reference may be made to U.S. Pat. No. 4,350,062, to Fan et al. This patent describes a power tong having a “C”-shaped power-driven rotary gear which turns within an outwardly containing tong body. The gap in the “C” serves as a throat through which pipe may be passed into the central body region of the tong.
The tong body also is “C”-shaped to allow pipe to be centered within the tong for rotation. While reference will be made to a “C”-shaped power tong in this disclosure, the invention is equally applicable to tongs that have a closed circular central opening through which pipe is inserted endwise.
The rotary gear within the tong body of a power tong has an inwardly-directed camming surface formed along its inner circular face. This cam surface generally provides two or more inwardly extending crescent-shaped circular wedge portions intended to help the gripping jaws engage with the pipe. The jaws are carried within a respective jaw carrier that includes a cam follower roller which rides along the cam surface, forcing the jaws inwardly until pipe is engaged. The outer circumference of the rotary gear contains gear teeth for engagement with a drive train mounted within the tong body to effect rotation of rotary gear, jaws and engaged pipe.
In operation the rotary gear drives one or more jaws carried in respective jaw assemblies, through the cam follower roller, into engagement with centrally-positioned pipe as the rotary gear begins to turn with respect to the tong body. The jaws within the jaw assemblies are contained between cage plates that cap the upper and lower sides of the central opening in the rotary gear. These cage plates “float” on the outer upper and lower surfaces of the tong body, free for partial rotation with respect to the rotary gear about their common center. The outer circumferential edges of the cage plates traditionally overlie the edges of the upper and lower plates of the tong body surrounding the central opening and the cage plates are free to rotate with respect to the tong body. They are constrained to remain centered but are free to rotate about the same axis as the pipe, but only for a portion of a full revolution with respect to the rotary gear until the jaw or jaws have engaged pipe. Thereafter the cage plates and jaw carrier or carriers and associated jaws rotate with the rotary gear. The camming surface and jaw carrier dimensions are selected to ensure pipe engagement and limit differential rotation between the cage plates and the rotary gear, generally to within less than a quarter-circle of rotation.
When the rotary gear first begins to turn after pipe has been placed in the center of the tong, a brake temporarily constrains the cage plates from rotating in conjunction with the gear. As the rotary gear commences to turn, the cam followers on the jaw assemblies are advanced radially inward by the camming surfaces of the rotary gear. This inward advancement arising from differential rotation between the cage plates with their jaws and the rotary gear continues until the jaws engage with the drill pipe. Further advancement of the cam followers up the inwardly advancing cam surfaces locks the jaws to the pipe and arrests further relative rotation between the cage plates and the rotary gear. Thereafter, the pipe is turned by the continued rotation of the rotary gear and jaw assemblies together, the force to effect rotation being transmitted through the jaws which are engaged with the pipe.
When the jaws are not in use, each jaw may be withdrawn from the central portion of the tong by the “parking” of each of the cam follower's rollers into a respective neutral recess formed in the inside surface of the rotary gear. Each such neutral recess is located adjacent to a beginning portion of the camming surface so that a cam follower's roller may retire into and nest within it. This allows the jaws to swing outwardly from the tong centre and frees the pipe to be slid inwardly or outwardly, through the throat in the “C”-shaped tong body, or to be inserted centrally in the case of a closed tong body.
The proper grasping of the drill pipe by the jaws depends on the relative rate of advancement of the jaws inwardly as the cam follower moves along the cam surface. The cam surface may be envisaged as a kind of curved wedge that is forced against the cam follower roller to urge the associated jaw inwards toward the pipe to is be gripped. As with a wedge, the rate of increase of the inward gripping force applied by the jaws as the cam follower moves up the cam surface will depend upon the steepness of the cam surface. This relative incline ratio of the cam surface may be characterized as the “camming schedule”.
Once the jaws have contacted the pipe, a relatively high radial force is applied to the pipe in order to ensure that a non-slipping, frictional engagement persists while torque is applied to the pipe. High torque forces are required to be applied to pipe in order to ensure that the joints in the drill pipe are properly made up, to break such joints, and to turn the drill pipe string where the boring of the earth is occurring if the power tong is used for such purpose. Such torque is applied to the rotary gear through a gear train that is typically driven by a hydraulic motor mounted on the tong body.
High radial forces are achieved by providing an appropriately powered hydraulic motor and gear train. As the camming surface is generally provided with a gradual inwardly-directed slope along which the camming roller is required to advance, as the jaws engage the pipe and are urged to force rotation of the pipe, a substantial spreading force is applied to the rotary gear along its inner camming surfaces. This outwardly directed force has to be contained. At the same time, it is important to ensure that the rotary gear continues to be free to rotate within the power tong body in engagement with the powered gear train. In particular, the rotary gear should be confined centrally within the power tong for rotation about the center of the central opening in the power tong throughout these actions.
Radial Containment of the Rotary Gear
Over a considerable range of torque values, the rotary gear of a power tong can be made sufficiently robust to resist outward expansion on its own. Nevertheless, a rotary gear needs to be constrained for rotation about a central location within the power tong body. For this reason, peripheral containment or rotary gear support rollers have traditionally been provided within the tong body.
In the past, to provide radial confinement for the rotary gear roller bearings have been provided that are mounted between the top and bottom covers of the tong body. Such roller bearings have in many cases been rotatably mounted within openings drilled in such covers. These rotary gear support roller bearings have been “dumbbell” like in shape and generally each dumbbell has been provided with two roller portions which extend around the gear teeth and engage against respective outward-directed circular track surfaces serving as races on the respective upper and lower sides of the ring gear. Such tracks have traditionally been located just above and below the gear teeth to support the rotary gear symmetrically about a central horizontal plane. An example of such a configuration is shown in FIG. 2 of U.S. Pat. No. 5,435,213, to Buck for a “Ring gear camming member” wherein the rollers 23 “bear against and contain a smooth surface 32 on ring gear 15, providing resistance to spreading when jaw members 4 are engaged with pipe 3”.
The roller bearings mounted inside the top and bottom covers of the tong body extend inwardly from the top and bottom inner surfaces of the cover plates to engage with a circular bearing surface on the rotary gear. The prior art configuration for supporting rotary gears has led to tongs of a significant thickness. Because the support rollers contact the rotary gear in pairs that embrace the centrally positioned gear teeth formed around the outer periphery of the rotary gear, such support roller pairs to take-up space between the rotary gear and the top and bottom on face plates. This increases the weight and/or cost of such tongs.
It would be desirable to establish a new configuration for supporting rotary gears which would allow a power tong to be built which is of reduced size and weight. This invention addresses that objective.
Specific Prior Art Rotary Gear Support
U.S. Pat. No. 4,827,808 to Haynes et al. issued May 9, 1989 for a “Rotor to assembly for power tong” describes a tong configuration wherein the rotary gear support rollers are mounted on the underside of the rotary gear, aligned to roll against a guide track carried by the bottom plate of the tong body. In particular, the support rollers are carried on posts or “stubs” protruding downwardly from the lower face of the rotary gear. The guide track contacted by the support rollers is fitted to the topside surface of the bottom cover of the tong body, and therefore the support rollers are located in the space between the rotary gear and the bottom cover. No portion of the rotary gear support rollers extends through the central opening defined by this bottom plate. An extension of the guide track is also carried by the gate at a location inwards from the levels of the tong covers. Additionally, this prior art reference is an example of providing a-symmetrical support for a rotary gear. The support rollers for the rotary gear as depicted are only present on the lower side of the rotary gear. Having cam followers on one side only as seen in this invention reduces the radial load carrying capacity of the rotary gear assembly and therefore limits applications but is nevertheless available as an option.
While U.S. Pat. No. 4,827,808 does describe a tong wherein a roller guide means for centering the rotary gear is mounted on the gear itself, nevertheless the thickness of the tong body of this configuration is increased by the fact that the rotary gear support rollers engage with the track fitted within the interior of the tong body, on the topside surface of the bottom cover of the tong body. This is particularly apparent in FIG. 3 of this reference which shows the extension of the guide track mounted on the inside surface bottom cover of the gate.
Central Alignment of the Cage Plates
Cage plates need to be centered on a power tong body as well. Cage plates can be centered on the tong either by guides mounted on the upper or lower covers of the tong body, or by guides provided by the rotary gear. In U.S. Pat. No. 5,819,604 to Buck, as seen in FIG. 3, rollers are fitted to the cage plates in a circumferential array. These rollers on the respective cage plates extend into receiving cavities, machined as accurate slots, formed in the top and bottom faces of the ring gear. These rollers keep the cage plates centered with respect to the rotary gear.
As an alternative to using rollers for centering the cage plate, Canadian patent 1,327,825 to McCoy et al, entitled “Track Supported Cage Plates for Power Tongs”, describes a rail and track combination as a centering means for a cage plate assembly. The rail is a circular ring formed on the outside of the tong body, and the track is a groove formed on the inside surfaces of the cage plates, or conversely. As described, the rail is preferably formed of a high-impact, abrasion resistant, low-friction elastomeric polymeric material, such as polyurethane.
Some form of centering arrangement for cage plates must generally be present in a power tong of this type. The present invention also addresses this objective.
Rotary Gear Support Across the Gate
In the standard “C”-shaped power tong, support rollers for the rotary gear are mounted in the body of the tong extending around the circular opening within the tong, from one side of the tong throat to the other. Support rollers are not generally included in the gate that closes such throat. In most applications, when the rotary gear turns in such tongs there is a portion of its outside periphery, adjacent to the throat of the tong, that is unsupported.
It would be desirable to provide support for the rotary gear in this region, namely in the region of the throat of the power tong. This invention addresses that objective.
Confinement of Rotary Gear Against Vertical Displacement
While peripheral roller bearings traditionally supply support to ensure the centering of a rotary gear in the plane of the gear, a rotary gear is also normally confined against vertical displacement within the tong body. In the past rotary gears have been confined by a bearing ring carried on the inside face of one or both of the cover plates of the tong body, as for example in U.S. Pat. No. 3,261,241 to Catland, items 48, 50, FIGS. 4, 5. This present invention addresses a further way to provide confinement for the rotary gear against vertical displacement within the tong body.
Gate Latch Mechanism
In a “C”-shaped power tong provided with a gate to close the opening or throat in the power tong, it is important to ensure that the gate is properly latched and secure before commencing operation of the tong. U.S. Pat. No. 4,827,808 to Haynes et al. depicts a latch 32 in FIG. 1. U.S. Pat. No. 6,082,224 to McDaniels, et al. depicts in FIG. 1A a feature described as “Safety interlock prevents tong from operating unless properly latched”.
The gate can be latched mechanically, in which circumstances it would be desirable to provide a detection mechanism to detect whether or not the gate is latched. Alternately, the latching of the gate can be effected by a power actuated latching system. In the past, such a hydraulically-based latching mechanism has relied upon hydraulic components located on the tong body adjacent to the gate or throat. This is an inconvenient location for either a power actuated latching system or a latch interlocked detection mechanism as this location makes such components vulnerable to collision with pipes and tools that may be present in the vicinity of the throat. It would be desirable to provide an arrangement by which a power actuated latching system or latching detection mechanism on a power tong is provided through components located at a more secure location.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the accompanying drawings. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.